Embodiments of the invention relate generally to pressure sensors for automotive use.
Residues from crankcase oil vapor can pass through a pressure sensor housing port as shown in FIG. 1A and reach the bottom surface of a pressure sensing element diaphragm as depicted in FIG. 1B and form deposits there.
FIG. 1A is a cross-sectional view of a pressure sensor in accordance with the prior art. The pressure sensor includes a pressure sensing element 100, a cover 102, an application-specific integrated circuit (“ASIC”) 106, a port 108, an O-ring 110, and a housing 114.
FIG. 1B is a cross-sectional view of a pressure sensing element 100 in accordance with the prior art. The pressure sensing element 100 including a silicon substrate 116, and a glass pedestal 122 anodically bonded to each other is mounted onto a housing substrate 126 using adhesive 124. The silicon substrate 116 is etched to form a cavity 120 from the bottom side and a diaphragm 118 at the top side.
FIG. 2A is a top view of a pressure sensing element 100. P+ conductive silicon interconnects 200 connect a picture-frame transducer 202 (or micro-Wheatstone bridge) that includes four piezoresistors to Vn 204, Sp 206, Vp 208, and Sn 210.
FIG. 2B shows the four piezoresistors, R1-R4, of the picture-frame transducer 202.
FIG. 3 shows the backside 302 and the edge 304 of the diaphragm 118. Enough accumulation of residue 300 on the backside of the diaphragm, as shown in FIG. 3, can induce stresses on the piezoresistors on the top side of the pressure sensing element thereby undesirably causing a voltage shift, which negatively affects sensing accuracy. As such, improved techniques for preventing accumulation of crankcase oil vapor residue would advance the art.